A guide wire is employed to guide a catheter used for treating a site where access to a surgical operation or procedure is difficult such as, for example, PTCA (Percutaneous Transluminal Coronary Angioplasty) or for treating the human body in a minimally-invasive manner, or for examination purposes such as cardiovascular contrast imaging. A guide wire used for PTCA is inserted together with a balloon catheter, in a state in which the distal end of the guide wire projects outwardly from the distal end of the balloon catheter, into a portion in the proximity of a vasoconstrictive site which is a target site.
Blood vessels can have shapes that curve in rather complicated ways. Thus, for a guide wire used when a balloon catheter is inserted into a blood vessel, the guide wire must have flexibility and resilience against suitable flexure, pushability and torque transmission performance for transmitting an operation force at the proximal portion to the distal side (these are generally referred to as “steerability”), kink resistance (flexural resistance) and other characteristics. Possible constructions for obtaining suitable flexibility, among the characteristics mentioned above, include a structure including a metal coil having flexibility against flexure disposed around a thin distal core member of a guide wire, or a structure which includes a superelastic wire of Ni—Ti or the like for a core member of a guide wire in order to provide the guide wire with flexibility and resilience.
A core member of a guide wire is made of substantially one kind of material, and in order to increase the steerability of the guide wire, a material having a comparatively high coefficient of elasticity is used. As a result of this, there the flexibility of the guide wire distal portion tends to be lost. On the other hand, if a material having a comparatively low coefficient of elasticity is used to obtain flexibility of the distal portion of the guide wire, there is a loss in the steerability on the proximal side of the guide wire. It has thus been difficult to achieve both the required flexibility and the required steerability with one kind of core member.
To achieve improvements against drawbacks such as those described above, for example, a guide wire has been proposed in which a first wire disposed on the distal side and having flexibility and a second wire disposed on the proximal side and having high rigidity are connected to each other by soldering.
This guide wire achieves improvement in steerability by increasing the flexibility on the distal side and increasing the rigidity on the proximal side.
However, a solder material itself made of an Ag—Cu based alloy, which is a popularly used material for soldering, is relatively low in mechanical characteristics such as flexural strength. Thus, when the guide wire is curved, there is the possibility that the soldered portion may be broken or bent.
Further, where the first wire and the second wire are individually covered with an oxide film, upon soldering, the oxide film cannot get wet with the solder material. Therefore, it is difficult to firmly solder the first wire and the second wire to each other.